The present invention relates to a magnetic disc device wherein a magnetic disc is housed in a casing.
A magnetic disc device as illustrated In U.S. Ser. No. 292,447, now U.S. Pat. No. 4,445,157 will first be described with reference to FIGS. 1, 2A and 2B, in which FIG. 1 is an exploded perspective view of the device and FIGS. 2A and 2B are respectively a top view and a bottom view of the same. Referring to these figures, a flexible magnetic disc 1 consists of a thin, disc-shaped base film of a high polymeric material and a magnetic layer uniformly formed at least on the bottom surface of the base film. A center plate 2 is fitted in a circular hole at the center of the magnetic disc 1 through a ring-shaped double-coated adhesive tape 3. The center plate has a flange 4 and is formed by pressing a thin metal plate. The magnetic disc 1 is adhered to the flange 4. A motor shaft receiving hole 5 of a polygonal shape is formed at the center of the center plate 2. A position regulating pin receiving hole 6 of a rectangular shape is also formed in the center plate 2 at a predetermined distance from the motor shaft hole 5.
The magnetic disc 1 with the center plate 2 is housed within a casing consisting of an upper shell 7 and a lower shell 8. These shells 7 and 8 are injection-molded from, for example, an ABS resin containing an antistatic agent and are adhered together at the peripheries by means of conventional ultrasonic sealing. The center plate is fit with a small clearance into circular opening 9 formed at the center of the lower shell 8. Four arc-shaped ribs 10 extend on the inner surface of the lower shell 8 concentrically with the opening 9, and four arc-shaped ribs which correspond to the above-mentioned ribs 10 are similarly formed on the inner surface of the upper shell 7.
Liners 11 and 12 of unwoven fabric such as rayon are adhered to the inner surfaces of the upper and lower shells 7 and 8 by heat sealing or ultrasonic sealing. The liners 11 and 12 serve automatically to remove dust deposited on the magnetic disc 1 and prevent dropout of signals from the disc during rotation, as well as to prevent abrasion and generation of static electricity of the magnetic disc 1. The liner 12 is adhered on the inner surface of the lower shell over a tongue 13 of a synthetic resin, so that the liner 12 is securely urged against the magnetic surface of the magnetic disc 1.
Elongated head access holes 14, 15, 16, 17 of identical shape are formed in the upper shell 7, the lower shell 8, the liner 11 and liner 12 respectively and extend in the radial direction of the magnetic disc 1. When the upper and lower shells 7 and 8 are joined together, these elongated head access holes are registered with each other. Upon loading the magnetic disc into a magnetic disc recorder, a magnetic head is brought into contact with the magnetic disc 1 through the elongated head access hole 17 formed in the lower shell 8 and the elongated head access hole 16 formed in the liner 12. Similarly, a head pad is inserted into the elongated head access hole 14 formed in the upper shell 7 and into the elongated head access hole 15 formed in the liner 11.
Recesses 18 and 19 are formed on those parts of the upper and lower shells 7 and 8 which include the elongated head access holes 14 and 17, respectively. A U-shaped aluminum shutter 20 which has openings 21 and 22 of the same shape as that of the elongated holes 14 to 17, is slidably mounted such that it clips into the recesses 18 and 19.
As shown in FIG. 2B, a guide groove 23 is formed along the side edge of the lower shell 8. Three protuberances 24 project inwardly from the shutter 20 to cooperate with the guide groove 23. Therefore, the shutter 20 is guided along the guide groove 23 between the operating state and the non-operating state. Referring to FIGS. 2A and 2B, in the operating state, the shutter 20 is moved to the position where the edge thereof coincides with the side walls on one side of the recesses 18 and 19. Thus, the elongated holes 16 and 17 for head insertion, the elongated holes 14 and 15 for head pad insertion, and the holes 21 and 22 are all registered as indicated by the solid lines, and the magnetic disc 1 is exposed therethrough. On the other hand, in the non-operating state, the shutter 20 is moved to the position where the edge thereof coincides with the side walls on the other side of the recesses 18 and 19. In that condition, the elongated holes 14 to 17 are closed and the magnetic disc 1 is covered by the shutter 20, as indicated by the dotted line. In this manner, the shutter 20 serves to protect the magnetic disc 1 and prevent introduction of dust. Notch 30 is formed on the position corresponding to the edges of the upper and lower shells 7 and 8, this notch 30 is arranged to be opened or closed depending on the sliding of the shutter 20. The notch 30 is made open only when the shutter 20 is open, in other cases it is closed. The notch 30 is used for detecting the shutter position so as to enable the loading of the magnetic disc device into a disc recorder only when the shutter 20 is open.
An erroneous erasure prevention lug 25 is further arranged at one corner of the lower shell 8. Information recorded on the magnetic disc 1 is protected if the lug 25 is removed. As shown in FIG. 2B, a pair of positioning holes 26 and 27 are formed at two corners of the lower shell 8 for positioning the magnetic disc device in a disc recorder. At the other two corners of the lower shell 8, holes are not formed, but positions 28 and 29 indicated by hatched lines in FIG. 2B serve as reference surfaces. Thus, the magnetic device is supported at the reference position with reference to the four points. In this state, the magnetic disc 1 is rotated by a motor to record or reproduce digital signals or analog signals.
Small holes 31A and 31B are formed on the opposite corners from the protuberances 24 of the shutter 20 as mentioned above, as shown in FIG. 2B. On the other hand, small hemisphere-shaped projections 32A and 32B are formed in the recess 19 of the lower shell 8. In the opening position of the shutter 20, the projection 32A enters the small hole 31A. Similarly in the closing position of the shutter 20, the projection 32B enters the small hole 31B. This engagement of the projection 32A and the hole 31A or of the projection 32B and the hole 31B causes a detent, or click effect between the casing and the shutter, securing them in the relatively fixed condition. FIGS. 3A and 3B show sectional side view of the shutter 20 and a part of the casing in the opening state. In FIGS. 3A and 3B, the magnetic disc 1, liners 11 and 12, etc. to be enclosed in the shell are not shown.
In such a magnetic disc device, however, the click effect occurs near the center of the shell, so that such a portion near the center of the lower shell 8 is so flexible that the upper and lower shells 7 and 8 must be strongly sandwiched by the shutter 20 for sufficient click effect. To be concrete, the upper and lower shells 7 and 8 are strongly and elastically sandwiched by the shutter 20 by using the shutter 20 whose opening width is smaller than the distance between the outermost surfaces of upper shell 7 and lower shell 8. As shown in FIG. 3B, the sandwiching force of this shutter 20 in the directions indicated by the arrows in FIG. 3A causes the shells 7 and 8 to be warped inwardly. Therefore, the distance between both shells 7 and 8 near the center of the magnetic disc device becomes narrow, so that the smooth rotation of the center plate 2 (and a magnetic disc) disposed at the opening 9 of the shells 7 and 8 may be impossible. This results in the overload of the motor on rotating the magnetic disc 1. In the worst case, the failure of rotation of the magnetic disc may also occur.
To avoid such problems, the present applicant has proposed a magnetic disc device which has a construction as shown in FIG. 4 in which a clicking projection 33 is formed in the guide grooves 23 at both ends within the range where the protuberances 24 of the shutter 20 can slide. In such a casing, since no click portion is formed at the center of the shell, enough click effect can be obtained without any deformation of the shells. Thus, it is possible to prevent the overload on rotating the magnetic sheet or a failure of rotation thereof. However, increase in the number of sliding operations of the shutter 20 causes the projection 33 to be scraped off by the protuberances 24, resulting in loss of the initial clicking force. There is also a problem in which a stable click force is not obtained since the heights of the protuberances are not uniform.